Matthew Clark, 29, pretended he had caught the fish in a sea fishing contest and was photographed smiling proudly next to his catch.

However, another competitor smelt something fishy when he recognised the prize-winning fish from a recent family visit to the aquarium. He alerted staff, who confirmed that the fish was indeed missing, and the competition organisers were informed.

Clark, from St Sampson, Guernsey, admitted to charges of burglary and fraud, and was ordered by a judge on Thursday to carry out 100 hours of community service.

Guernsey magistrates court also heard that Clark had previously worked at the Guernsey Aquarium at St Peter Port, on the isle of Guernsey, and had planned to break in and steal the fish in order to win the £800 prize money and use his winnings to pay back a debt he owed the aquarium owner.

He was forced to take an oath of good behaviour for two years – and faces jail if he breaks the terms of the sentence.